Markdown is a markup language with plain text formatting syntax designed so that it can be converted to HTML and many other formats using a tool by the same name.

Markdown allows you to write using an easy-to-read, easy-to-write plain text format, which then converts to valid HTML for viewing on GitHub, StackOverflow?, Reddit etc.

See for detail: ​http://en.wikipedia.org/wiki/Markdown

Tutorials

1. An short online interactive tutorial: ​http://markdowntutorial.com/
2. Example on Wikipedia: ​http://en.wikipedia.org/wiki/Markdown#Example
3. Materials on GitHub:
   • ​Markdown Basics
   • ​GitHub Flavored Markdown
   • ​Writing on GitHub